1. Field of the Invention
The present invention is directed to a control installation for a device for a dental apparatus which has at least one part which is adjustable to selected positions out of a plurality of positions by operation of a drive motor. The control installation utilizes a comparison of an actual value indication to a nominal value indication to produce an error signal utilized to control the operation of the motor.
2. Prior Art
In the case of known control installations which are provided for the purpose of controlling the operation or movement of a dental treatment chair, electro-mechanical transmitters or emitters in the form of potentiometers are utilized as a nominal value and an actual value indicators or transmitters. Examples of these installations are shown in U.S. Pat. Nos. 3,866,973 and 3,984,146. The positioning and adjustment of the potentiometers as well as the programming of the nominal or reference value indicators is relatively costly. In addition, the electro-mechanical actual value indicators of these type devices are inclined to malfunctions.
In another known type of control installation for positioning of an adjustable object such as a chair seat, the desired position is determined by reading a punch card which is inserted into the control installation. Such a device is disclosed in German Offenlegungsschrift No. 2,119,837. Aside from the fact that the handling of the punch cards is comparatively unwieldy because a particular punch card must first be taken from a separate file or storage place, the cards of this type are subject to wear and other distortions. In addition, the transfer installations requires means for scanning the respective punch card which, in addition, represents an interference factor in the chair construction.